Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
LEDs where a majority of light is extracted through the top of the device may be formed by molding a reflective material around the sides of the device, to prevent light from escaping from the sides. Molding is illustrated in FIG. 1, which is described in more detail in US 2011/0018017. FIG. 1 illustrates the submount wafer 360 and LEDs 100 attached to the submount. Lines are drawn on the wafer 360 illustrating where the wafer 360 will be later sawed or broken for singulation.
A mold 400, also known as a chase, has indentions 420 that are preferably shallow to ensure that the tops of the LEDs contact or come very close to the flat bottom surface of each indention 420. The indentions 420 are slightly wider than the LEDs 100, where the difference will be the thickness of the molded material covering the sides of the LEDs 100. A viscous mixture 440 of silicone and TiO2 is precisely dispensed over the mold 400 to fill the indentions 420 and also create a thin layer between the indentions 420. The submount wafer 360 and mold 400 are brought together under pressure so that the LEDs 100 are immersed in the mixture 440. When the tops of the LEDs 100 are just touching the bottoms of the indentations 420, pressure is maintained and the silicone is cured, such as by heating. The wafer 360 and mold 400 are then separated, and the hardened silicone/TiO2 460 may be further cured by heating or UV. The submount wafer 360 is then singulated along the lines by sawing or breaking.
The relatively thick layer of silicone/TiO2 covering the sides of the LED 100 reflects substantially all of the LED side light (e.g., at least 75%). After any reflection off the silicone/TiO2 sidewall, a portion of the reflected light will ultimately exit through the top surface of the LED 100 (the top surfaces of the LEDs 100 are facing down in the orientation illustrated in FIG. 1).